U.S. patent application number 10/227630 was filed with the patent office on 2003-03-27 for switching power supply circuit.
This patent application is currently assigned to Fuji Electric Co., Ltd.. Invention is credited to Igarashi, Seiki.
Application Number | 20030058664 10/227630 |
Document ID | / |
Family ID | 19082013 |
Filed Date | 2003-03-27 |
United States Patent
Application |
20030058664 |
Kind Code |
A1 |
Igarashi, Seiki |
March 27, 2003 |
Switching power supply circuit
Abstract
A switching power supply circuit reduces the capacity of the
capacitor on the load side, reducing its size, weight, and cost.
The switching power supply circuit has a pair of diodes connected
in series, a pair of MOSFETs connected in series, a pair of
capacitors connected in series, a snubber capacitor connected in
parallel with the pair of diodes, the pair of MOSFETS, and the pair
of capacitors. The circuit can include a pair of additional
capacitors, connected respectively in parallel with the MOSFETS, to
allow the MOSFETs to execute a zero-voltage switching. The circuit
also includes an AC input terminal connected to the mutual
connection point of the pair of diodes, a transformer including a
primary winding having one end connected to the mutual connection
point of the pair of MOSFETS, and the other end connected to the
mutual connection point of the pair of capacitors. The primary
winding has a center tap connected to another AC input
terminal.
Inventors: |
Igarashi, Seiki; (Tokyo,
JP) |
Correspondence
Address: |
ROSSI & ASSOCIATES
P.O. Box 826
Ashburn
VA
20146-0826
US
|
Assignee: |
Fuji Electric Co., Ltd.
|
Family ID: |
19082013 |
Appl. No.: |
10/227630 |
Filed: |
August 23, 2002 |
Current U.S.
Class: |
363/56.12 |
Current CPC
Class: |
H02M 3/337 20130101 |
Class at
Publication: |
363/56.12 |
International
Class: |
H02H 007/122 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 24, 2001 |
JP |
JP2001-253737 |
Claims
What is claimed is:
1. A switching power supply circuit comprising: a transformer
having a primary winding with a center tap and a secondary winding;
a pair of diodes connected in series; a pair of switching devices
connected in series; a pair of capacitors connected in series; a
snubber capacitor; a first AC input terminal connected to both of
the pair of diodes; and a second AC input terminal connected to the
center tap of the primary winding, wherein the snubber capacitor,
the pair of diodes, the pair of switching devices, and the pair of
capacitors are connected in parallel, wherein one end of the
primary winding is connected to both of the pair of switching
devices, and wherein the other end of the primary winding is
connected to both of the pair of capacitors.
2. The switching power supply circuit according to claim 1, further
including a rectifying circuit connected to the secondary winding
of the transformer.
3. A switching power supply circuit comprising: a switching means
for converting a single-phase AC input voltage to a high-frequency
AC voltage; a transformer for insulating the high-frequency AC
voltage, wherein the transformer comprises a primary winding having
a center tap and a secondary winding, a rectifying circuit for
rectifying the insulated high-frequency AC voltage to feed DC
electric power to a load; a first circuit comprising two diodes
connected in series; a second circuit comprising two switching
devices connected in series; a third circuit comprising a first
capacitor and a second capacitor connected in series; a snubber
capacitor, wherein the snubber capacitor, the first circuit, the
second circuit and the third circuit are connected in parallel; a
first AC input terminal connected to a common connection point of
the two diodes in the first circuit; and a second AC input terminal
connected to the center tap of the primary winding, wherein one end
of the primary winding is connected to the common connection point
of the switching devices of the second circuit, wherein the other
end of the primary winding is connected to the common connection
point of the first capacitor and the second capacitor of the third
circuit, and wherein the rectifying circuit is connected to the
secondary winding of the transformer.
4. The switching power supply circuit according to claim 3, further
including at least one capacitor connected in parallel with at
least one of the switching devices, wherein the at least one
capacitor allows at least one of the switching devices to execute a
zero-voltage switching.
5. The switching power supply circuit according to claim 3, wherein
the switching power supply circuit adjusts an ON-OFF duty ratio of
one of the switching devices to regulate the current of the AC
input voltage, and the switching power supply circuit adjusts the
operating frequency of the other of the switching devices to
regulate the DC electric power.
6. The switching power supply circuit according to claim 4, wherein
the switching power supply circuit adjusts an ON-OFF duty ratio of
one of the switching devices to regulate the current of the AC
input voltage, and the switching power supply circuit adjusts the
operating frequency of the other of the switching devices to
regulate the DC electric power.
Description
BACKGROUND
[0001] FIG. 5 is a diagram showing a conventional switching power
supply circuit described in "High-Frequency Isolation UPS with
Novel SMR" (IECOM '93, pp. 1258-1263, (1993)). Such a conventional
switching power supply circuit includes a first series circuit
including diodes D.sub.1 and D.sub.2 connected in series, a second
series circuit including MOSFETs Q.sub.1 and Q.sub.2 connected in
series, and a third series circuit including MOSFETs Q.sub.3 and
Q.sub.4 connected in series. The conventional switching power
supply circuit also includes a snubber circuit SN connected in
parallel with the first through third series circuits.
[0002] A first AC input terminal U is connected to the common
connection point of the diodes D.sub.1 and D.sub.2. A primary
winding section P.sub.1 of a transformer T.sub.1 having center taps
is connected to the common connection point of the MOSFETs Q.sub.1
and Q.sub.2. The other primary winding section P.sub.2 of the
transformer T.sub.1 is connected to the common connection point of
the MOSFETs Q.sub.3 and Q.sub.4. The center tap between the primary
winding sections P.sub.1 and P.sub.2 of the transformer T.sub.1 is
connected to a second AC input terminal V.
[0003] The secondary winding sections S.sub.1 and S.sub.2 of the
transformer T.sub.1 are connected to an end of a capacitor C.sub.5
via diodes D.sub.3 and D.sub.4, respectively. The center tap
between the secondary winding sections S.sub.1 and S.sub.2 of the
transformer T.sub.1 is connected to the other end of the capacitor
C.sub.5. DC output terminals P and N are connected to the capacitor
C.sub.5.
[0004] When the transformer T.sub.1 (the primary winding sections
P.sub.1 and P.sub.2) is short circuited by switching ON the MOSFETs
Q.sub.1 and Q.sub.3 while the AC input voltage is positive, the
current of a reactor L.sub.1 increases. When the MOSFET Q.sub.3 is
switched OFF in the state described above, the reactor current
flows through the primary winding section P.sub.1 from the MOSFET
Q.sub.1, feeding electric power to the capacitor C.sub.5 via the
secondary winding section S.sub.1 and the diode D.sub.3.
[0005] When the transformer is short circuited again by switching
ON the MOSFET Q.sub.3, the reactor current increases. When the
MOSFET Q.sub.1 is switched OFF subsequently, the reactor current
flows through the MOSFET Q.sub.3. The reactor current flowing
through the MOSFET Q.sub.3 excites the primary winding section
P.sub.2 of the transformer T.sub.1, and electric power is fed to
the capacitor C.sub.5 via the secondary winding section S.sub.2 and
the diode D.sub.4.
[0006] By repeating the operations described above at a high
frequency, the AC input voltage is insulated and converted to DC
electric power by the transformer T.sub.1. The insulated and
converted DC electric power is output via the diodes D.sub.3,
D.sub.4 and the capacitor C.sub.5. When the AC input voltage is
negative, the conventional switching power supply operates in the
same manner as described above by switching ON and OFF the MOSFETs
Q.sub.2 and Q.sub.4.
[0007] The conventional switching power supply circuit employs four
MOSFETs Q.sub.1 through Q.sub.4, a reactor L.sub.1, and a snubber
circuit SN. Since it is necessary for the conventional switching
power supply circuit to incorporate four driving circuits, each
driving any of the MOSFETs Q.sub.1 through Q.sub.4, the size of the
conventional switching power supply circuit is large and the cost
thereof is high. Since there exits certain time points where the
single-phase AC input voltage is zero, the energy fed to the load
is interrupted, causing large ripple voltages on the load. For
obviating this problem, it is necessary for the capacitor C.sub.5
on the load side to have a sufficiently large capacity. Therefore,
the size of the conventional switching power supply circuit is
further enlarged and the cost thereof increased even further.
[0008] Accordingly, there is a need for a switching power supply
circuit that at least reduces the capacity of the capacitor on the
load side to reduce its size, weight, and cost. The present
application addresses this need.
SUMMARY OF THE INVENTION
[0009] The present invention relates to a switching power supply
circuit. The switching power supply circuit can have a transformer,
a pair of diodes, which can form a first circuit, a pair of
switching devices, which can form a second circuit, a pair of
capacitors, which can form a third circuit, a snubber capacitor,
and first and second AC input terminals.
[0010] The transformer can have a primary winding with a center tap
and a secondary winding. The pair of diodes are connected in
series, as are the pair of switching devices and the pair of the
capacitors. The first AC input terminal is connected to both diodes
or the common connection point of the two diodes. The second AC
input terminal is connected to the center tap of the primary
winding. The snubber capacitor, the pair of diodes, the pair of
switching devices, and the pair of capacitors are connected in
parallel. One end of the primary winding is connected to both
switching devices or the common connection point of the switching
devices. The other end of the primary winding is connected to both
capacitors or the common connection point of the pair of
capacitors.
[0011] The switching power supply circuit can further include a
rectifying circuit, which can be connected to the secondary winding
of the transformer, and a switching means for converting a
single-phase AC input voltage to a high-frequency AC voltage. The
transformer can insulate the high-frequency AC voltage. The
rectifying circuit can rectify the insulated high-frequency AC
voltage to feed DC electric power to a load.
[0012] The switching power supply circuit can further include at
least one capacitor connected in parallel with at least one of the
switching devices, wherein the at least one capacitor allows at
least one of the switching devices to execute a zero-voltage
switching. The switching power supply circuit can adjust an ON-OFF
duty ratio of one of the switching devices to regulate the current
of the AC input voltage and the operating frequency of the other of
the switching devices to regulate the DC electric power.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a diagram of a switching power supply circuit
according to the first embodiment of the invention.
[0014] FIG. 2 is a diagram of a switching power supply circuit
according to the second embodiment of the invention.
[0015] FIGS. 3(a) through 3(d) are circuit diagrams illustrating
the current paths of the MOSFETs shown in FIG. 1.
[0016] FIG. 4 shows the wave forms of the voltages and the currents
at certain points of the circuit shown in FIG. 1.
[0017] FIG. 5 is a diagram of a conventional switching power supply
circuit.
DETAILED DESCRIPTION
[0018] Now the invention will be described in detail hereinafter
with reference to the accompanied drawings, which illustrate the
preferred embodiments of the invention. The same reference numerals
and symbols designate the same or similar elements
[0019] Referring to FIG. 1, which is a diagram of a switching power
supply circuit according to a first embodiment of the invention,
the switching power supply circuit includes a first series circuit,
which includes diodes D.sub.1 and D.sub.2 connected in series with
each other, a second series circuit, which includes MOSFETs Q.sub.1
and Q.sub.2 connected in series with each other, a third series
circuit, which includes a first capacitor C.sub.1 and a second
capacitor C.sub.2 connected in series with each other, and a
snubber capacitor C.sub.S. The first series circuit, the second
series circuit, the third series circuit and the snubber capacitor
C.sub.S are connected in parallel with each other. A third
capacitor C.sub.3 is connected in parallel with the MOSFET Q.sub.1
and a fourth capacitor C.sub.4 with the MOSFET Q.sub.2. The third
capacitor C.sub.3 or the fourth capacitor C.sub.4, however, can be
omitted.
[0020] A first AC input terminal U is connected to both diodes
D.sub.1 and D.sub.2 or the common connection point of the diodes
D.sub.1 and D.sub.2. An end of the primary winding P of a
transformer T.sub.1 having center taps is connected to both MOSFETs
Q.sub.1 and Q.sub.2 or the common connection point of the MOSFETs
Q.sub.1 and Q.sub.2. The other end of the primary winding P of the
transformer T.sub.1 is connected to both capacitors C.sub.1 and
C.sub.2 or the common connection point of the capacitors C.sub.1
and C.sub.2. The center tap of the primary winding P is connected
to a second AC input terminal V. An end of a capacitor C.sub.5 is
connected to both ends of the secondary winding S of the
transformer T.sub.1 via the diodes D.sub.3 and D.sub.4. The other
end of the capacitor C.sub.5 is connected to the center tap of the
secondary winding S of the transformer T.sub.1. The primary winding
P of the transformer T.sub.1 is divided by the center tap thereof
into two sections P.sub.1 and P.sub.2. The secondary winding S of
the transformer T.sub.1 is divided by the center tap thereof into
two sections S.sub.1 and S.sub.2. Leakage inductance LK.sub.1 and
LK.sub.2 on the primary side of the transformer T.sub.1 and DC
output terminals P and N connected to the capacitor C.sub.5 are
shown in FIG. 1.
[0021] Now the operations of the switching power supply circuit
according to the first embodiment will be described with reference
to FIGS. 3(a) through 3(d) and FIG. 4. FIGS. 3(a) through 3(d) are
circuit diagrams describing the current paths caused by the ON and
OFF cycling of the MOSFETs Q.sub.1 and Q.sub.2. FIG. 4 shows the
wave forms of the voltages and the currents at certain points of
the circuit shown in FIG. 1.
[0022] By switching ON the MOSFET Q.sub.1 while the AC input
voltage is positive, a current i.sub.1 is made to flow, as
illustrated by the solid curve in FIG. 3(a), from the AC input
terminal U to the AC input terminal V via the diode D.sub.1, the
MOSFET Q.sub.1, and the primary winding section P.sub.1 of the
transformer T.sub.1, storing energy in the leakage inductance
LK.sub.1 of the primary winding of the transformer T.sub.1. At the
same time, a current i.sub.2 is made to flow, as illustrated by the
dotted curve in FIG. 3(a), from the capacitor C.sub.S to the
capacitor C.sub.2 via the MOSFET Q.sub.1 and the primary winding
sections P.sub.1, P.sub.2 of the transformer T.sub.1, discharging
the energy stored so far in the capacitor C.sub.S to the secondary
side via the transformer T.sub.1.
[0023] By switching OFF the MOSFET Q.sub.1, a current i.sub.3 is
made to flow, as illustrated by the solid curve in FIG. 3(b), from
the AC input terminal U to the AC input terminal V via the diode
D.sub.1, the capacitor C.sub.S, the capacitor C.sub.4, and the
primary winding section P.sub.1 of the transformer T.sub.1, storing
energy in the capacitor C.sub.S and discharging the capacitor
C.sub.4. At the same time, a current i.sub.4 is made to flow from
the capacitor C.sub.S to the capacitor C.sub.2 via the capacitor
C.sub.3 and the primary winding sections P.sub.1 and P.sub.2 of the
transformer T.sub.1, charging up the capacitor C.sub.3. When the
MOSFET Q.sub.1 is switched OFF during the operations described
above, the voltages at both ends of the capacitor C.sub.3 are zero.
The zero-voltage switching reduces the switching loss.
[0024] By switching ON the MOSFET Q.sub.2, a current i.sub.5 is
made to flow, as illustrated in FIG. 3(c), from the capacitor
C.sub.S to the capacitor C.sub.S via the capacitor C.sub.1, the
primary winding sections P.sub.2 and P.sub.1 of the transformer
T.sub.1, and the MOSFET Q.sub.2, discharging the energy stored in
the capacitor C.sub.S to the secondary side of the transformer
T.sub.1 via the primary winding P thereof.
[0025] By switching OFF the MOSFET Q.sub.2, a current i.sub.6 is
made to flow, as illustrated in FIG. 3(d), from the capacitor
C.sub.S to the capacitor C.sub.4 via the capacitor C.sub.1 and the
primary winding sections P.sub.2 and P.sub.1 of the transformer
T.sub.1, charging up the capacitor C.sub.4, and a current i.sub.7
is made to flow from the capacitor C.sub.3 to the capacitor C.sub.3
via the capacitor C.sub.1 and the primary winding sections P.sub.2
and P.sub.1 of the transformer T.sub.1, discharging the capacitor
C.sub.3. When the MOSFET Q.sub.2 is switched OFF during the
operations described above, the voltages at both ends of the
capacitor C.sub.4 are zero. The zero-voltage switching reduces the
switching loss.
[0026] In the switching power supply circuit according to the first
embodiment, the zero-voltage switching operations of the MOSFETs
Q.sub.1 and Q.sub.2 are facilitated by charging and discharging the
capacitors C.sub.3 and C.sub.4 connected respectively in parallel
with the MOSFETs Q.sub.1 and Q.sub.2. After the operations
described with reference to FIG. 3(d) are over, the operations
described in FIGS. 3(a) through 3(d) are repeated. Thus, by
switching ON and OFF the MOSFETs Q.sub.1 and Q.sub.2 at a high
frequency, the primary winding P of the transformer T.sub.1 becomes
excited and unexcited repeatedly, and the current having the wave
form as shown in the bottom portion of FIG. 4 is output from the DC
output terminals P and N via the secondary winding S of the
transformer T.sub.1 and the diodes D.sub.3 and D.sub.4.
[0027] According to the first embodiment, the magnitudes of the AC
input current and the current for charging up the capacitor C.sub.S
are regulated by adjusting the ON period of the MOSFET Q.sub.1. The
electric power feed to the load is regulated by adjusting the ON
periods of the MOSFETs Q.sub.1 and Q.sub.2. Therefore, the AC input
current can be controlled by adjusting the ON-OFF duty ratio of the
MOSFET Q.sub.1. The electric power feed to the load or the output
voltage can be controlled by adjusting the ON period and the OFF
period, i.e., the operating frequency of the MOSFET Q.sub.2, once
the ON period of the MOSFET Q.sub.1 is set.
[0028] While the AC input voltage is negative, the switching power
supply circuit according to the first embodiment operates in the
same manner as described above by exchanging the operation of the
MOSFET Q.sub.1 and the operation of the MOSFET Q.sub.2 with each
other. In other words, the energy is stored in the leakage
inductance LK.sub.2 by switching ON the MOSFET Q.sub.2 in FIG.
3(a). The MOSFET Q.sub.2 is switched OFF in FIG. 3(b). The MOSFET
Q.sub.1 is switched ON in FIG. 3(c) and switched OFF in FIG.
3(d).
[0029] Energy is stored in the leakage inductance LK.sub.1 of the
primary winding P and the energy stored in the snubber capacitor
C.sub.S is discharged by switching ON one of the switching devices
Q.sub.1, Q.sub.2. Energy is stored in the snubber capacitor C.sub.S
by switching OFF the same switching device. The energy stored in
the snubber capacitor C.sub.S is discharged by switching ON the
other of the switching devices Q.sub.2, Q.sub.1. Since it is
possible to discharge the energy stored in the snubber capacitor
C.sub.S by switching ON the switching device even when the AC input
voltage is zero, it becomes possible to reduce the ripple voltage
without interrupting the electric power to be output. Therefore, it
is not necessary for the capacitor C.sub.5 on the load side to have
a large capacity. Since the energy stored in the capacitor C.sub.S
is discharged to the load during the period T.sub.L, for that the
AC input voltage is low as shown in FIG. 4, and since the capacitor
C.sub.S is charged up while the electric power is fed to the load
during the period T.sub.H, for that the AC input voltage is high,
the ripple voltage is reduced without interrupting the electric
power to be output.
[0030] FIG. 2 is a diagram of a switching power supply circuit
according to a second embodiment of the invention. The switching
power supply circuit according to the second embodiment is
different from the switching power supply circuit according to the
first embodiment in that the capacitors C.sub.3 and C.sub.4
incorporated in the switching power supply circuit according to the
first embodiment are omitted from the switching power supply
circuit according to the second embodiment. Since the currents for
charging and discharging the capacitors C.sub.3 and C.sub.4 do not
exist according to the second embodiment, the MOSFETs Q.sub.1 and
Q.sub.2 do not execute zero-voltage switching. However, the
operations associated with the switching of the MOSFETs Q.sub.1 and
Q.sub.2, such as the discharge of the energy stored in the
capacitor C.sub.S, are conducted in the same manner as those of the
switching power supply circuit according to the first embodiment
shown in FIG. 1. The switching power supply circuit according to
the second embodiment further reduces component count, simplifying
the circuit configuration.
[0031] Although the switching power supply circuit according to the
first embodiment or the second embodiment has been described in
connection with the center-tap-type full-wave rectifying circuit
for the rectifying circuit on the secondary side of the transformer
T.sub.1, the other rectifying circuits, such as a half-wave
rectifying circuit, a full-wave rectifying circuit employing four
diodes and a fly-back-type rectifying circuit may be applied.
[0032] Although it is necessary for the conventional switching
power supply circuit to employ four switching devices, it is enough
for the switching power supply circuit according to the invention
to employ only two switching device. The switching power supply
circuit according to the invention thus simplifies the driving
circuits, while using the leakage inductance of the transformer in
place of the input side reactor. Therefore, the switching power
supply circuit according to the invention can reduce the
components, and thus reduces the size, weight, and cost.
[0033] Since the switching power supply circuit according to the
invention feeds electric power continuously, the switching power
supply circuit according to the invention reduces the voltage
ripples caused by the discontinuous electric power feed from the
conventional switching power supply circuit and reduces the
capacity of the capacitor on the load side. Therefore, the size,
weight, and cost of the switching power supply circuit are further
reduced. Moreover, the switching power supply circuit that executes
zero-voltage switching facilitates to reduce the switching loss,
improving the electric power conversion efficiency and down-sizing
the cooling apparatus.
[0034] Given the disclosure of the present invention, one versed in
the art would appreciate that there may be other embodiments and
modifications within the scope and spirit of the present invention.
Accordingly, all modifications and equivalents attainable by one
versed in the art from the present disclosure within the scope and
spirit of the present invention are to be included as further
embodiments of the present invention. The scope of the present
invention accordingly is to be defined as set forth in the appended
claims.
[0035] The disclosure of the priority application, JP PA
2001-253737, in its entirety, including the drawings, claims, and
the specification thereof, is incorporated herein by reference.
* * * * *